Self Potentials In Cave Detection

In this presentation, we show an example of the use of self potential geophysics to locate<br>caves or voids. We develop a simple model of water flow where a cavity is a preferential<br>drainage path generating streaming potentials above the local groundwater flow. Two<br>temporal data sets with the same positions were collected at the Indian Echo Caverns<br>located in Hershey, Pennsylvania. One was in dry conditions and the second, one year<br>later, with the ground saturated with rainfall. The data was gathered using the gradient<br>method and later processed by integration. The data set in the dry conditions shows a<br>single anomaly located over a known cave location and the data set in the wet conditions<br>has several anomalies. Both sets show groundwater flow feeding into a nearby river.<br>The differences of the two data sets are due to the change in resistivity of the soil caused<br>by rainwater and the enhancement of very near surface infiltration paths of rainwater.<br>We show that SP can be used for cave detection under the proper conditions.